They aren't completely isolated. It's a relatively short boat ride to get to Crisfield. It's kind of similar to any small town of that size that has a larger city nearby. There's some intermingling and some people that travel back and forth regularly.

It's largely diminished. The advent of TV and radio means they get much more exposure to mainstream accents now. I've been to the island and if I hadn't already been told to keep my ears open for it, their accent wouldn't have sounded any different from a typical Eastern Shore accent to me.

Not everyone celebrates Christmas. I'm not Christian, so I've only vaguely heard the term "12 Days of Christmas" and "Advent" before. Never with enough context for me to know anything about it other than them vaguely being associated with Christmas I've never heard the term "Christmastide" before your comment and the term "Epiphany" just sort of vaguely means "having a sudden idea". I've never heard it used in a religious context before.

Everyone knew the Armistice was coming. Setting the specific time for it was to give everyone time to spread the word to avoid confusion. By 10:59, everyone had been informed and was just waiting for the clock to tick down. This guy didn't want to live in a world without the war. Maybe he thought it was one last chance for glory, maybe he was severely depressed, maybe he had a psychotic break, or maybe something else. We will never know exactly what was going through his head, just that everyone around him though he was crazy and tried to stop him. The Germans only shot him after waving him off and telling him to stand down didn't work.